nginx.conf
add/increase client_max_body_size in the nginx configuration file http area/section:
http {
client_max_body_size 32m;
(other lines will also be here)
}

reference:
http://wiki.nginx.org/HttpCoreModule#client_max_body_size


php.ini
Check and/or increase the following:
upload_max_filesize = 32M
post_max_size = 32M

Optionally increase:
max_execution_time =300
max_input_time=300
memory_limit =128M

Restart nginx or your server for the changes to take effect after applying changes. The default client_max_body_size is 1 megabyte so most likely your theme is larger than 1 mb and you need to increase it to an amount larger than the size of the theme you are trying to install.

Otherwise, you could most likely upload your theme by ftp instead if it's available.

Additionally you can set the above examples to suit your needs.

I want to ask you i add line in server but when i go to save file with ctrl x i am unable to save ,can u tell me how to save nginx conf file?
vim /etc/nginx/nginx.conf.

If you're using vim, you need to press Escape, type :wq, and press Enter to save a file.